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<title>Reading RTL (GNU Compiler Collection (GCC) Internals)</title>

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Previous: <a href="Sharing.html" accesskey="p" rel="prev">Structure Sharing Assumptions</a>, Up: <a href="RTL.html" accesskey="u" rel="up">RTL Representation</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html" title="Index" rel="index">Index</a>]</p>
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<h3 class="section" id="Reading-RTL-1"><span>14.23 Reading RTL<a class="copiable-link" href="#Reading-RTL-1"> &para;</a></span></h3>

<p>To read an RTL object from a file, call <code class="code">read_rtx</code>.  It takes one
argument, a stdio stream, and returns a single RTL object.  This routine
is defined in <samp class="file">read-rtl.cc</samp>.  It is not available in the compiler
itself, only the various programs that generate the compiler back end
from the machine description.
</p>
<p>People frequently have the idea of using RTL stored as text in a file as
an interface between a language front end and the bulk of GCC.  This
idea is not feasible.
</p>
<p>GCC was designed to use RTL internally only.  Correct RTL for a given
program is very dependent on the particular target machine.  And the RTL
does not contain all the information about the program.
</p>
<p>The proper way to interface GCC to a new language front end is with
the &ldquo;tree&rdquo; data structure, described in the files <samp class="file">tree.h</samp> and
<samp class="file">tree.def</samp>.  The documentation for this structure (see <a class="pxref" href="GENERIC.html">GENERIC</a>)
is incomplete.
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